# Triangle angle properties

9 videos

3 skills

Do the angles in a triangle always add up to the same thing? Would I ask it if they didn't? What do we know about the angles of a triangle if two of the sides are congruent (an isosceles triangle) or all three are congruent (an equilateral)? This tutorial is the place to find out.

### Proof: Measures of interior angles of a triangle sum to 180°

VIDEO
6:31 minutes

Sal gives a formal proof that the measures of interior angles of a triangle sum to 180°.

### Triangle angle example 1

VIDEO
6:03 minutes

Figuring out angles in a triangle. A little about exterior angles being the sum of the remote interior angles

### Triangle angle example 3

VIDEO
5:42 minutes

Multiple ways to solve for the angles of multiple triangles

### Challenging triangle angle problem

VIDEO
8:37 minutes

Interesting problem finding the sums of particular exterior angles of an irregular pentagon

### Proof: Corresponding angle equivalence implies parallel lines

VIDEO
5:18 minutes

Proof by contradiction that corresponding angle equivalence implies parallel lines

### Finding angle measures 1

PRACTICE PROBLEMS

### Finding angle measures 2

PRACTICE PROBLEMS

### Sum of interior angles of a polygon

VIDEO
9:10 minutes

Showing a generalized way to find the sum of the interior angles of any polygon

### Angles of a polygon

PRACTICE PROBLEMS

### Sum of the exterior angles of convex polygon

VIDEO
5:24 minutes

More elegant way to find the sum of the exterior angles of a convex polygon